Phosphoramide mustard, an active metabolite of cyclophosphamide, has been reacted separately with guanosine and deoxyguanosine in aqueous solution at pH 7.4. The major adduct which was formed in each case has been isolated by reverse-phase high-pressure liquid chromatography. The structure of the major adduct, as determined by a combination of ultraviolet and field desorption mass spectrometry, is that of phosphoramide mustard, one arm of which has reacted with guanosine or deoxyguanosine in position 7. These adducts are much less stable than was 7-methylguanosine, and they decompose with a half-life of 2.3 hr at 37° and pH 7.4. This instability may contribute to the action of phosphoramide mustard at a molecular level.

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Supported by Grants CA 20129 and CA 20292 from the National Cancer Institute, Department of Health, Education, and Welfare, and by Grant PTB 8207 for drug development from the Bundesministerium für Forschung und Technologie, Bonn, West Germany.

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